Processor-controlled systems, for example systems controlled by microprocessors or microcontrollers, are especially used for realizing particular applications, for example for realizing prescribed functions or process sequences. Through an error in the system, for example, through a malfunction in the processor or a bit error in a memory unit of the system, an application error can arise, for example an erroneous process sequence or an unintended function can be realized and carried out. This erroneous behavior or malfunction is undesired and interfering, and must be excluded or prevented especially in processor-controlled systems for realizing safety critical applications (in motor vehicles for example the applications relating to the cruise control, the airbag, or the steering angle recognition, or control devices influencing the motor of the motor vehicle).
In order to recognize and/or exclude erroneous behaviors or malfunctions of the system, especially in safety critical applications, the processor can be monitored by an external monitoring unit, especially by an external monitoring computer or an external application specific circuit (ASIC); the system is reset, or switched to be non-functional, or switched into a secure condition, if a malfunction of the processor is recognized by the external monitoring unit. In this regard, the difficulties in the synchronization of the processor and the external monitoring unit, the problems that are possible in the communication between the processor and the external monitoring unit, especially potential EMC interferences on the connecting lines between the processor and the external monitoring unit, the additional costs for the external monitoring unit as well as the expenditures and efforts for hardware, development and programming of the external monitoring unit, are all disadvantageous.